1. Field
The present invention relates to anaerobic cure systems containing enamines, their use as cure accelerators for anaerobic adhesive compositions, and anaerobic adhesive compositions including such enamine cure accelerators.
2. Brief Description of Related Technology
Anaerobic adhesive compositions generally are well-known. See e.g. R. D. Rich, “Anaerobic Adhesives” in Handbook of Adhesive Technology, 29, 467-79, A. Pizzi and K. L. Mittal, eds., Marcel Dekker, Inc., New York (1994), and references cited therein. Their uses are legion and new applications continue to be developed.
Conventional anaerobic adhesives ordinarily include a free-radically polymerizable acrylate ester monomer, together with a peroxy initiator and an inhibitor component. Oftentimes, such anaerobic adhesive compositions also contain accelerator components to increase the speed with which the composition cures.
Desirable anaerobic cure-inducing compositions to induce and accelerate cure may include saccharin, toluidines, such as N,N-diethyl-p-toluidine and N,N-dimethyl-o-toluidine, acetyl phenylhydrazine (“APH”), maleic acid, and quinones, such as napthaquinone and anthraquinone. See e.g. U.S. Pat. Nos. 3,218,305 (Krieble), 4,180,640 (Melody), 4,287,330 (Rich) and 4,321,349 (Rich).
In addition, other curatives for anaerobic adhesives include thiocaprolactam (e.g., U.S. Pat. No. 5,411,988) and thioureas [e.g., U.S. Pat. No. 3,970,505 (Hauser) (tetra methyl thiourea), German Patent Document Nos. DE 1 817 989 (alkyl thioureas and N,N′-dicyclohexyl thiourea) and 2 806 701 (ethylene thiourea), and Japanese Patent Document No. JP 07-308,757 (acyl, alkyl, alkylidene, alkylene and alkyl thioureas)], certain of the latter of which had been used commercially up until about twenty years ago.
Loctite (R&D) Ltd. owns a new class of materials—trithiadiaza pentalenes—effective as curatives for anaerobic adhesive compositions. The addition of these materials into anaerobic adhesives as a replacement for conventional curatives (such as APH) surprisingly provides at least comparable cure speeds and physical properties for the reaction products formed therefrom. (See International Patent Publication No. WO 00/40664.)
In an unrelated field of technology, U.S. Pat. No. 5,503,936 (Blyakhman) describes and claims curable modified epoxy resin compositions having an epoxy resin, a hardener or curing agent and 2.5 to 12.5% by weight of a compound represented by
where E and T are C5-12 alkyl, C5-8 cycloalkyl, C7-15 phenylalkyl, or C6-10 aryl, with or without substitution by one or two C1-4 groups. The hardeners or curing agents of the '936 patent are described as aliphatic, aromatic or cycloaliphatic di- or polyamines, such as diethylenetriamine, N-aminoethylpiperazine, 4,4′-diaminodicyclohexylmethane, 4,4′-diaminodiphenyl sulfone, diethyldiaminotoluene, dicyandiamide, or guanidine; polycarboxylic acid anhydrides, such as phthalic anhydride or trimellitic anhydride; catalytic curing agents such as tertiary amines, imidazoles or complexes of boron trifluoride; difunctional and multifunctional phenols; or phenol or cresol novolac resins.
In addition, a number of suppliers including Flexsys America, Akron, Ohio, Sumitomo Chemical, Osaka, Japan, and Crompton Corporation, Waterbury, Conn. sell phenylene diamine type anti-oxidants, which are promoted to retard oxidation, degradation, or pre-mature polymerization.
Henkel Corporation recently developed an anaerobic anaerobic adhesive composition, comprising:                (a) a (meth)acrylate component;        (b) an anaerobic cure-inducing composition; and        (c) the following phenylene diamine-based cure accelerator:        
where R and R1 may be the same or different and may be selected from C1-12 alkyl, C1-12 alkenyl, C5-12 cyclo or bicycloalkyl, C6-18 aryl, and derivatives thereof, and is C6-18 arylene, and derivatives thereof and oxidized versions thereof. [See U.S. Pat. No. 6,723,763 (Zhu).]
There is an on-going desire to find alternative technologies to differentiate existing products and provide supply assurances in the event of shortages or cessation of supply of raw materials. Accordingly, it would be desirable to identify new materials which function as accelerators in the cure of anaerobic adhesives.